Radiotherapy is a form of cancer treatment which involves the application of radiation directed to a particular situs in a patient's body. The applied radiation destroys targeted cancer cells. However, the radiation can also affect some of the normal cells nearby. Where the radiotherapy is used to treat cancers of the head and neck, the destruction and damage of nearby healthy tissue can result in severe side effects due to the presence of many critical structures and organs in that part of the body. For this reason, it is very important that radiation is targeted as far as possible so as to destroy only the cancerous cells whilst leaving other nearby structures intact.
Devices immobilising the position of a patient's head and neck are used to improve the accuracy and reproducibility of positioning the head and neck in medical diagnostic and treatment procedures. These devices are particularly important when a patient is undergoing fractionated radiation therapy where radiation is applied to a patient on a number of different occasions. When undergoing fractionated treatment it is important to try to ensure that a patient is placed in the same position for each treatment session so that the same location can be irradiated throughout the course of treatment.
One of the simplest approaches to assist a patient to maintain their position is with use of a chin strap. However, this approach fails to immobilise the head and neck completely which increases the chances of a patient moving during a treatment session and hence the dangers of detrimental side affects. A simple chin strap also fails to ensure that a patient will be positioned consistently during the course of multiple treatment sessions.
To address this problem it is known to immobilise a patient's head using a full-face mask. Such a full-face mask is normally made out of a thermoplastic material which is heated prior to an initial treatment session. The mask is then moulded to a patient's head by being placed over the patient's face and then allowed to set. The resultant full-face mask completely encloses a patient's head and thus restricts movement and allows a patient to be placed into a fixed position for each treatment session. Examples of such full face masks are disclosed in WO03/061477and WO04/032781.
Although a full-face mask is an improvement on immobilising a patient solely with a chin strap existing masks suffer from a number of drawbacks.
As the mask covers the vast majority or the entirety of a patient's face with only small apertures for eyeholes, some patient's find existing masks claustrophobic and uncomfortable. Further, although the full-mask approach substantially limits a patient's movement as the mask encloses a patient's head, it is still possible for small movements to occur within the mask. Further as the mask completely obscures a patient's face it is not possible to monitor for movement during treatment.
An alternative head restraint for maintaining the position of a patient during a medical procedure such as imaging by position emission tomography (PET) or magnetic resonance imaging (MRI) is disclosed in WO00/27331. WO 00/27331 is an example of a prior art head restraint for use with a tracking system as such the face leaves a portion of the face unobscured. However the design of the mask of WO 00/27331 suffers from similar problems to the chinstrap prior art.
An alternative immobilisation assembly that assists with precise positioning of the patient's head during repeated and subsequent treatments and examinations whilst increasing a patient's comfort is therefore desirable.